Polychlorinated biphenyls (PCBs) are halogenated aromatic compounds that received widespread commercial use for almost 40 years. After this extended period of use it was discovered that they bioaccumulated in the environment and were toxic to wildlife. They have now been banned from commercial trade for over 20 years, but still persist as environmental contaminants. A primary mode of toxicity of PCBs to wildlife appears to disruption of endocrine function to result in altered reproductive cycles. Increased attention has been focused on this mechanism of toxicity as more sensitive assays have been developed. However, the toxicity of a given PCB is a function of its structural characteristics and it bioavailability from the environment. Though exposure to PCBs may be detected in a variety of matrices, soil contamination probably accounts for most of the PCBs in the environment. Most human and wildlife exposure to soil is dermal; therefore, these studies have been designed to determine the kinetics describing the bioavailability and fate of PCBs following dermal exposure. Since there are 209 possible PCBs depending on the degree and position of chlorination, selected congeners are being studied in order to determine the importance of degree and position of chlorination to bioavailability. For comparison, we are also determining the kinetics that describe the fate of these compounds following oral and iv exposure. These studies will eventually determine the effect of various types of soil on the bioavailability of the PCBs studied.